Reinforcement of hard rock strata as well as soft strata for preventing rock collapse is carried out using support systems incorporating rock bolts. The rock bolts are inserted into holes drilled into rock and secured there by resin or cement based grout applied in the holes.
To consolidate the separate steps of drilling a hole in rock then inserting and fixing a rock bolt in the drilled hole, self drilling rock bolts are used. Self drilling rock bolts can be drilled into rock and anchored therein in one pass.
Problems have occurred with both regular rock bolts and self drilling rock bolts where the rock bolts become loose from the grout and become unstable. This can occur as a result of movement in the rock strata or as a result of the load imparted on the rock bolt by the rock support system. Danger arises where a rock bolt becomes unstable because there is a possibility that the rock bolt will pull free of rock which can lead to rock collapse. Improving the safety of rock support systems and avoiding rock collapse are important issues in the mining and tunnelling industry.